Piezo pienzo..

During this week Forum we looked more in detail at the features of contact microphones...the so called 'piezos'.



Piezoelectric microphones contain ceramic or quartz crystals linked with a diaphragm or directly exposed to acoustic waves. Stresses in the crystals, resulting from a sound field, generate an output proportional to the acoustic pressure. The frequency response is not very whide of course but many designs incorporate a built-in preamplifier next to the crystal. This reduces the electrical noise and output impedance.

Piezoelectric microphone. AP = acoustic pressure, Uo = output voltage, 1 = diaphragm, 2 = ceramic or quartz crystals, 3 = built-in preamplifier, 4 = case

How funky is the sound of a window glass in a windy day? And the one of the linf running into the branch of a tree, how intense? What about the blood in your veins..?
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Mr. Piezo, as most in his family, have a double personality and can act as a microphone as well as a speaker - yeh yeh...
Running the sound through different objects you are physically filtering it and you can explore different characteristics of materials and shapes...
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Interestingly, during class, we occurred in a mysterious phenomenon that made us doubt about the fact that Bob Dylan ghost was between us..............?
We were playing one of Bob's song from a CD player into a small amplifier outputting into the piezo. I was holding this piezo near the piano in Studio 5 and Colin holding an other amplifier with a piezo connected near the mixer. The two amplifiers were not connected by any sort of lead but, when we were both touching the piezos, Bob Dylan was actually playing in Colin's ampli!!!
Buh...?
Apparently we occurred in an experience of 'induction'..... in the sense that our skin was the conductor (and our body the antenna) within this magic magnetic field we are all surrounded by....Anyway it was very funny!
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So, at the moment the idea is to construct a sort of 'piezo-gong' or even two (eventually to call back 'wireless-Bob'...).
With this, performers will be able to deploy their flesh properties in concertant movements...but how to deal with feedback ??
(I know...I'm obsessed...but I'm aware ok!?).
I've been looking with no luck for row materials... so now thinking about which kind of matter could be good for just expanding the surface... gold is kind of expensive even for Rotary!
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More: running the sound through the walls of a room produces a spatialisation phenomenon in which sound varies according to human presence and movement in the acoustic space...always for the same induction, I guess...I'd like to try...but no more pieos at Dick Smith and quite a few are needed (someone used up to 500!).
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Finally I found an interesting project called Sotavento :
'Sotavento is an artistic sound abstraction of the passionate and endless relationship between millions of trees and one single, inexorable wind, a wind that we all share. We establish an Internet-based, real-time movement communication between moving trees located in different countries. The trees' "dance" is tracked down by two dual-axis accelerometers, each fixed to the tip of a branch. We use the complex branch movements to generate or to trigger sounds. In this installation a tree is a self-replicant sound maker of its own dance. The audience can perceive the relation between the “dance” of the tree and the music it produces. Even is there is no wind, the tree in Mexico can “ask” (via Internet) for movements to a tree in Italy and generate its sounds with this information. The sounds are to be listened thanks to a set of four speakers installed around the tree.'


Hear:


References:
http://zone.ni.com/devzone/cda/ph/p/id/180
http://www.makezine.com/blog/archive/2007/08/sotavento_what_does_a_tre.html
http://en.wikipedia.org/wiki/Electromagnetic_induction